1. Field of the Invention
This invention relates to the field of communication systems, and more particularly, to calling devices that generate and play call progress tones.
2. Description of the Prior Art
When making a call, a caller may hear tones or message being played that indicate the status of a call. The tones are commonly referred to as call progress tones (CPT), which are audible tones or messages played to indicate the progress of a call. One example of a call progress tone is a slow busy signal that indicates that the called party is not available. Another example of a call progress tone is a fast busy signal that indicates that the system is busy. Another example of a call progress tone is a message stating that the line is busy.
A typical communication system is comprised of a calling device coupled to an originating system. The originating system is coupled to a Public Switched Telephone Network (PSTN). Examples of calling devices are telephones, cellular phones, computers, and fax machines. An example of the originating system is a class-5 switch.
A user of the calling device initiates a call to a called device in the PSTN through the originating system. The calling device transmits set up messages to the originating system. The originating system sets up the call by exchanging signaling with a terminating system connected to the called device. The terminating system transmits acknowledgment messages to the originating system to indicate the progress of the call. The acknowledgment messages inform the originating system whether the call can be completed. For instance, the acknowledgment messages indicate that the PSTN is busy, that the called device is busy, that the called device is being alerted, or some other event. The originating system processes the acknowledgment messages to determine the proper call progress tone for the call. The originating system generates and transmits the call progress tone to the calling device. The calling device plays audible sounds that represent the call progress tone so that the user of the calling device can hear it.
Unfortunately, the originating system generates the call progress tones and maintains the call to transmit the call progress tones, which increases the workload on the originating system. Consequently, the originating system does not effectively handle other calls, which could adversely affect the performance of the communication system.
This can be a particular problem in wireless networks. The originating system transmits the call progress tones over a frequency to a wireless phone. Frequencies and bandwidth are valuable commodities in a wireless network, and the originating system uses valuable bandwidth to transmit the call progress tones.